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In this study, we present a new species of freshwater mussel in the genus Postolata Dai et al., 2023, from Guangxi Province, China, by integrating morphological, anatomical, and molecular data. Postolata longjiangensis Liu & Wu, sp. nov. is distinguished from its congener (i.e., Postolata guangxiensis) by its shell shape, beak position, surface sculpture, nacre color, and hinge structure. Molecular species delimitation results based on the mitochondrial COI gene support the separation of Postolata longjiangensis Liu & Wu, sp. nov. from its congener. The multi-locus (COI + 16S rRNA + 28S rRNA) phylogeny reveals that this species forms the sister lineage to Postolata guangxiensis in the tribe Gonideini.

A new species of freshwater mussel belonging to the genus Pseudocuneopsis, namely Pseudocuneopsis wuana sp. nov., is diagnosed and described from Guangxi Province, China. This paper provides a detailed shell morphological description, soft-body anatomical characteristics, and partial sequences of mitochondrial COI as DNA barcode data for the novel species. The new species can be distinguished from its congeners (Pseudocuneopsis sichuanensis, P. yangshuoensis, and P. capitata) by shell shape, beak position, and surface sculpture. Phylogenetic analyses based on the mitochondrial COI gene reveal that Pseudocuneopsis wuana sp. nov. forms a sister group with P. yangshuoensis and exhibits an interspecific genetic distance of 5.1%. Therefore, we provide robust morphological and molecular evidence to support the validity of this new species.

A new species of freshwater mussel belonging to the genus Pseudocuneopsis, namely Pseudocuneopsis yangshuoensis sp. nov., is diagnosed and described from Guangxi Province, China. This paper provides a detailed morphological description, photograph of the type specimen, and anatomical characteristics along with partial sequences of mitochondrial COI as DNA barcode data for this novel species. The new species can be distinguished from its congeners (Pseudocuneopsis sichuanensis and Pseudocuneopsis capitata) by shell shape, beak position and surface sculpture. The interspecies genetic distance based on the COI barcode between P. yangshuoensis sp. nov. and P. sichuanensis is 8%, while it reaches 9% with P. capitata. Therefore, we provide robust morphological and molecular evidence to support the validity of this new species.

The worldwide decline in freshwater biodiversity due to rising anthropogenic pressures is of growing concern. Much evidence reveals that biodiversity loss and taxonomic homogenization results in loss of ecosystem functions. Understanding temporal and spatial patterns of biodiversity is, a major challenge in ecological conservation. Of all groups of threatened aquatic animals, freshwater mussels are responsible for critical trophic and non-trophic functions. Based on published inventories and field surveys, here we aim to evaluate whether freshwater mussel diversity, density and biomass has changed in the last 60 years, as well as the factors driving these patterns in different areas within the Poyang Lake basin, a global biodiversity hotspot in the middle reach of the Yangtze River. Results showed that alpha diversity has declined in the current period (2016–2020) as compared to diversity in the historical (1960–2003) and intermediate periods (2003–2014). Overall species richness declined by 28 % over 60 years. Density and biomass also declined by 79 % and 42 %, respectively. Population declines led to homogenization of freshwater mussel faunas. Additionally, there was a significant association between pH and alpha and beta diversity, suggesting that acidification related to intensive agriculture development may be one major factor behind mussel declines. In summary, this study provides new insights into the patterns and drivers of freshwater mussel population dynamics in the Poyang Lake basin. The results have implications for the design of freshwater protected areas to slow, and even reverse, current declines.

Abstract Background Classification of parasitic bopyrids has traditionally been based on morphological characteristics, but phylogenetic relationships have remained elusive due to limited information provided by morphological data and tendency for loss of morphological features as a result of parasitic lifestyle. Subfamily Argeiinae was separated from Bopyrinae based on morphological evidence, although the assignment of all genera has not been phylogenetically evaluated. Bopyroides hippolytes has been traditionally classified in Bopyrinae, but divergent morphological characters make this assignment questionable. To investigate the relationship of bopyrines, we sequenced the complete mitochondrial genome of B. hippolytes and four mitochondrial genes of two other Bopyrinae. Results The phylogenetic trees based on separate and combined cox1and 18S sequence data recovered Bopyridae as robustly monophyletic, but Bopyrinae as polyphyletic. Bopyroides hippolytes was a close sister to Argeia pugettensis, type species to Argeiinae. Mitochondrial phylogenomics also suggested that B. hippolytes was close to Argeiinae. We also found a novel gene order in B. hippolytes compared to other isopods. Conclusions Bopyroides hippolytes should be excluded from the Bopyrinae and has a close affinity with Argeia pugettensis based on molecular and morphological data. The conserved syntenic blocks of mitochondrial gene order have distinctive characteristics at a subordinal level and may be helpful for understanding the higher taxonomic level relationships of Isopoda.

We diagnose and describe a new freshwater mussel species of the genus Inversidens, I. rentianensis sp. nov. from Jiangxi Province, China based on morphological characters and molecular data. This paper includes a morphological description and photograph of the holotype, and partial sequences of mitochondrial COI as DNA barcode data.

Abstract Accurate species identification is crucial for developing conservation strategies for freshwater mussels, one of the most imperiled faunas in the world. Traditionally, mussel species description primarily relied on conchological characters. However, shell morphology has great variability, which leads to the complexity of species delimitation. As endemic species to China, Lamprotula caveata was originally described by Heude (1877). Lamprotula quadrangulosus and Lamprotula contritus were considered for synonymization of L. caveata based on shell variants in the early 20th century, which has been long debated due to lack of rigorous molecular analysis. Moreover, great morphological variation caused doubt whether there are cryptic species. In this study, we used a combined phylogenetic and morphometric approach to verify the validity of the synonymization of L. caveata. The results of molecular species delimitation showed that two molecular operational taxonomic units (MOTUs) were identified in Lamprotula spp., including the L. leaii lineage and the complex lineage (L. quadrangulosa, L. cornuumlunae, L. contritus, and L. caveata). Phylogenetic analyses revealed that L. cornuumlunae formed a basal monophyletic clade, whose divergence time was relatively recent (4.26 Ma [95% HPD = 1.91–7.22 Ma]), and L. contritus, L. caveata, and L. quadrangulosa formed a large polytomy group with very shallow branches. In the previous study, we have demonstrated the validity of L. cornuumlunae. The molecular evidences supported that the complex (L. quadrangulosa + L. contritus + L. caveata) was a valid species; L. quadrangulosa and L. contritus were synonyms of L. caveata. In addition, three morphospecies (L. quadrangulosa, L. contritus, and L. caveata) were aggregated without clear differentiation based on shell morphometric analysis. We confirmed multiple phenotypes in L. caveata for species identification and presumed that the phenotypic plasticity was a response to specific habitats. This study clarified the diversity and phylogeny of the Lamprotula group, which is a crucial step for developing new conservation and management strategies for this imperiled group.

Abstract Freshwater mussels provide important functions and services for aquatic ecosystems, but populations of many species have been extirpated. Information on biodiversity plays an important role in the conservation and management of freshwater mussels. The Xin River Basin is a biodiversity hotspot for freshwater mussels in China, with more than 43 species known, but populations of which are decreasing. Here, we quantify the diversity of freshwater mussels in the middle and lower reaches of the Xin River Basin and study the correlation of habitat characteristics and freshwater mussel diversity. Compared to the historical period, the number of species, density, and biomass of freshwater mussels decreased 33%, 83%, and 82% in the current period, respectively. Fifty two percent of recorded species were empty shells, and 14 native freshwater mussels were not found in the study area. Four species are currently listed as vulnerable species using IUCN criteria and their global status. The assemblage structure of freshwater mussels exhibits significant spatial differences, and there was a correlation with substrate and physicochemical parameters. The main tributary of the Xin River with higher freshwater mussel diversity should be established as one large protected area because the nestedness component was the main pattern of beta diversity. These results indicated freshwater mussel diversity was declining rapidly, which can help focus conservation effort for freshwater mussel biodiversity.

Dams and diversions are a primary threat to freshwater fish biodiversity, including the loss of species and restructuring of communities, often resulting in taxonomic homogenization (increased similarity) over time. Mitigating these impacts requires a strong scientific understanding of both patterns and drivers of fish diversity. Here, we test whether different components of fish biodiversity have changed in response to major dam construction, and whether these patterns are predictable as a function of key environmental factors in the Gan River Basin, China. The results showed that total and native species alpha diversity have declined from the historical period (pre-dam) to the current period (post-dam). A total of 29 native species are lost, while 6 alien species were gained over time. We found evidence for fish faunal homogenization in the Gan River Basin, with a slight (1%) increase in taxonomic similarity among river basins from the historical period to the current period. Additionally, we revealed significant associations between drainage length, drainage area, and average air temperature, and alpha and beta fish diversity. This study provides new insight into the patterns and drivers of fish biodiversity change in the broader Yangtze River Basin and helps inform management efforts seeking to slow, and even reverse, current trajectories of biodiversity change.

The Yangtze River Basin (Changjiang Basin) hosts one of the most diverse freshwater mussel assemblages on Earth. However, due to human activities this fauna is dramatically imperiled in this region, highlighting the need for urgent conservation measures. To better protect and conserve these taxa, it is crucial to understand the main drivers that control the diversity patterns, as well as the anthropogenic influence on these patterns. Here, we estimated distinct diversity metrics (i.e. species richness and alpha, gamma, and beta diversity) to analyze the spatial freshwater mussel diversity changes across 16 tributaries and lakes from the middle and lower Yangtze River Basin, in two periods: past 1962–2012 and present. For the past, mussel records were compiled from previous studies, for the present, we surveyed 565 sites for freshwater mussel presence and abundance within the 16 selected areas. We also assessed several climatic and geographical parameters to try to identify the main factors that modulate species composition across the study area. We show that from the historical to the present periods, species diversity experienced a significant decrease, registering, per river/lake, an average of 5.4 extirpations of species native to China and 3.9 of the Yangtze River Basin endemics. The gamma diversity of the whole study area and the alpha diversity of each of the studied rivers and lakes have also decreased during this period. The beta diversity values indicated a significant trend towards taxonomic homogenization over the last decades. Poyang and Dongting Lakes should be considered for protection given due to their high diversity and species loss given that nestedness in these lakes represented the main component of beta diversity.

Biomphalaria straminea is an invasive species in China and is one of the intermediate hosts of Schistosoma mansoni which results in the spread of schistosomiasis. Herein, we firstly report the complete mitochondrial genome of B. straminea. The full length of the mitochondrial genome is 13,652 bp. It consists of 37 typical animal mitochondrial genes, comprising 13 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes. The contents of each base in the complete mitochondrial genome are 33.28% A, 42.01% T, 10.85% C, and 13.87% G, with a high A + T content of 75.29%. Phylogenetic analysis showed that the relationship of B. straminea and Biomphalaria tenagophila was more closed.

The Yangtze River drainage in China is among the most species rich rivers for freshwater mussels (order Unionida) on Earth with at least 68 species known. The freshwater mussels of the Yangtze River face a variety of threats with indications that species are declining in abundance and area of occupancy. This study represents the first analyses of the genetic structure and diversity for the common and widespread freshwater mussel Nodularia douglasiae based on microsatellite DNA genotypes and mitochondrial DNA sequences. Phylogenetic analysis a fragment of the COI mitochondrial gene indicated that N. douglasiae collected from across the middle and lower Yangtze River drainage are monophyletic with N. douglasiae from Japan, Russia, and South Korea. The results of the analysis of both the mtDNA and microsatellite datasets indicated that the seven collection locations of N. douglasiae in the middle and lower Yangtze River drainage showed high genetic diversity, significant genetic differentiation and genetic structure, and stable population dynamics over time. Moreover, we found that the connections among tributaries rivers and lakes in the Yangtze River drainage were important in maintaining gene flow among locations that N. douglasiae inhabits. An understanding of the genetic structure and diversity of a widespread species like N. douglasiae could be used as a surrogate to better understand the populations of other freshwater mussel species that are more rare in the Yangtze River drainage. At the same time, these results could provide a basis for the protection of genetic diversity and management of unionid mussels diversity and other aquatic organisms in the system.

We consider a ratio-dependent predator-prey system with a mate-finding Allee effect on prey. The stability properties of the equilibria and a complete bifurcation analysis, including the existence of a saddle-node, a Hopf bifurcation, and, a Bogdanov-Takens bifurcations, have been proved theoretically and numerically. The blow-up method has been applied to investigate the structure of a neighborhood of the origin. Our mathematical results show the mate-finding Allee effect can reduce the complexity of system behaviors by making the complicated equilibrium less complicated, and it can be a destabilizing force as well, which makes the system has a high possibility of being threatened with extinction in ecology.

We consider a predator{prey system with nonmonotonic functional response and a hyperbolic type of mate-finding Allee effect on prey. A detailed mathematical analysis of the system, including the stability and a series of bifurcations (a saddle-node, a Hopf, and a Bogdanov{Takens bifurcation), has been given. The mathematical results show that the system is highly sensitive to the parameters and initial status. It exhibits a stable limit cycle, or different types of heteroclinic curves, or a homoclinic loop when parameters take suitable values. [ABSTRACT FROM AUTHOR]

Background: Amidst the escalating loss of global biodiversity, freshwater mussels (family Unionidae) have become one of the most imperiled animal groups. Acquiring more biological and phylogenetic information on understudied taxa constitutes a pivotal aspect of conservation biology. Consequently, a comprehensive examination was conducted on Koreosolenaia, Parvasolenaia, and Sinosolenaia from China encompassing morphology, anatomy, distribution, and molecular systematics to provide theoretical support for future species endangerment assessments and biodiversity conservation. Results: The shell characteristics of Koreosolenaia, Parvasolenaia, and Sinosolenaia were clearly distinct, and the soft-body morphology could also be easily distinguished from each other. The papillae of the incurrent aperture of Sinosolenaia iridinea, Sinosolenaia recognita, and Sinosolenaia oleivora, which were previously described as difficult, exhibited significant variations that could be utilized for species diagnosis. Furthermore, both incurrent and excurrent apertures of the Sinosolenaia species had small cysts on their dorsal surfaces which may be unique to this particular group. Comparative analysis of six mitochondrial genomes (Parvasolenaia rivularis, Koreosolenaia sitgyensis, Sinosolenaia iridinea, Sinosolenaia recognita, Sinosolenaia carinata, and Sinosolenaia oleivora) revealed a completely consistent gene arrangement pattern. Additionally, there was a high consistency in nucleotide base content and skewness, amino acid usage, and relative synonymous codon usage among the six complete mitochondrial genomes. Mitochondrial phylogenomics of these genomes with additional taxa within Gonideinae robustly supported the generic relationships as follows: (Inversidens + ((Microcondylaea + Sinosolenaia) + (Parvasolenaia + (Koreosolenaia + (Ptychorhynchus + (Postolata + Cosmopseudodon)))))). Conclusions: The present study provided significant data on the shell morphology and soft-body anatomy of Koreosolenaia, Parvasolenaia, and Sinosolenaia, thereby clarifying the diagnostic characteristics for these challenging taxa. Additionally, we established a robust phylogenetic framework at both the generic and species levels based on mitochondrial genomics. [ABSTRACT FROM AUTHOR]

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Accurate phylogenetic reconstructions are crucial for comprehending the evolutionary histories, reproductive traits, and ecological habits of organisms. The subfamily Gonideinae of freshwater mussels is currently thought to include eight tribes. However, due to inadequate taxon sampling and molecular data, the assignment of the freshwater mussel genus Inversidens at the tribe level has been unstable. Additionally, the lack of phylogenetic data has hindered efforts to understand the basic biology and implementation of conservation efforts of Inversidens rentianensis, an endemic species to China. Here, we first present the complete mitochondrial genome of Inversidens rentianensis and offer a detailed description of its anatomical morphology. Based on DNA sequence data from five genes (COI, ND1, 16S rRNA, 18S rRNA, and 28S rRNA) and complete mitochondrial genomes, we investigated the phylogenetic position of Inversidens using various analytical methods. Both the concatenated five-gene and mitogenome datasets strongly supported that Inversidens classified to the tribe Gonideini in Gonideinae and formed a basal clade within the tribe Gonideini. Molecular dating analysis suggested that Inversidens originated during the mid-Cretaceous era (102.73 Mya, 95% highest posterior density HPD = 72.22 ‐ 137.03 Mya) and underwent diversification in the Late Paleogene era (37.92 Mya, 95% HPD = 20.39 ‐ 60.59 Mya). Moreover, based on the Quantitative Assessment of Species for Conservation (QASCP), Inversidens rentianensis is ranked as second priority, providing valuable insights for its management and conservation efforts. Taken together, this study provides a comprehensive understanding of the systematic position and evolutionary history of Inversidens within the currently accepted subfamily Gonideinae classification framework. These findings establish a solid foundation for future investigations on the ecology, reproductive behavior patterns, and conservation biology of this taxonomic group. [ABSTRACT FROM AUTHOR]

Accurate species identification is crucial for developing conservation strategies for freshwater mussels, one of the most imperiled faunas in the world. Traditionally, mussel species description primarily relied on conchological characters. However, shell morphology has great variability, which leads to the complexity of species delimitation. As endemic species to China, Lamprotula caveata was originally described by Heude (1877). Lamprotula quadrangulosus and Lamprotula contritus were considered for synonymization of L. caveata based on shell variants in the early 20th century, which has been long debated due to lack of rigorous molecular analysis. Moreover, great morphological variation caused doubt whether there are cryptic species. In this study, we used a combined phylogenetic and morphometric approach to verify the validity of the synonymization of L. caveata. The results of molecular species delimitation showed that two molecular operational taxonomic units (MOTUs) were identified in Lamprotula spp., including the L. leaii lineage and the complex lineage (L. quadrangulosa, L. cornuumlunae, L. contritus, and L. caveata). Phylogenetic analyses revealed that L. cornuumlunae formed a basal monophyletic clade, whose divergence time was relatively recent (4.26 Ma [95% HPD = 1.91–7.22 Ma]), and L. contritus, L. caveata, and L. quadrangulosa formed a large polytomy group with very shallow branches. In the previous study, we have demonstrated the validity of L. cornuumlunae. The molecular evidences supported that the complex (L. quadrangulosa + L. contritus + L. caveata) was a valid species; L. quadrangulosa and L. contritus were synonyms of L. caveata. In addition, three morphospecies (L. quadrangulosa, L. contritus, and L. caveata) were aggregated without clear differentiation based on shell morphometric analysis. We confirmed multiple phenotypes in L. caveata for species identification and presumed that the phenotypic plasticity was a response to specific habitats. This study clarified the diversity and phylogeny of the Lamprotula group, which is a crucial step for developing new conservation and management strategies for this imperiled group. [ABSTRACT FROM AUTHOR]

Dams and diversions are a primary threat to freshwater fish biodiversity, including the loss of species and restructuring of communities, often resulting in taxonomic homogenization (increased similarity) over time. Mitigating these impacts requires a strong scientific understanding of both patterns and drivers of fish diversity. Here, we test whether different components of fish biodiversity have changed in response to major dam construction, and whether these patterns are predictable as a function of key environmental factors in the Gan River Basin, China. The results showed that total and native species alpha diversity have declined from the historical period (pre-dam) to the current period (post-dam). A total of 29 native species are lost, while 6 alien species were gained over time. We found evidence for fish faunal homogenization in the Gan River Basin, with a slight (1%) increase in taxonomic similarity among river basins from the historical period to the current period. Additionally, we revealed significant associations between drainage length, drainage area, and average air temperature, and alpha and beta fish diversity. This study provides new insight into the patterns and drivers of fish biodiversity change in the broader Yangtze River Basin and helps inform management efforts seeking to slow, and even reverse, current trajectories of biodiversity change. [ABSTRACT FROM AUTHOR]

Background: Classification of parasitic bopyrids has traditionally been based on morphological characteristics, but phylogenetic relationships have remained elusive due to limited information provided by morphological data and tendency for loss of morphological features as a result of parasitic lifestyle. Subfamily Argeiinae was separated from Bopyrinae based on morphological evidence, although the assignment of all genera has not been phylogenetically evaluated. Bopyroides hippolytes has been traditionally classified in Bopyrinae, but divergent morphological characters make this assignment questionable. To investigate the relationship of bopyrines, we sequenced the complete mitochondrial genome of B. hippolytes and four mitochondrial genes of two other Bopyrinae. Results: The phylogenetic trees based on separate and combined cox1and 18S sequence data recovered Bopyridae as robustly monophyletic, but Bopyrinae as polyphyletic. Bopyroides hippolytes was a close sister to Argeia pugettensis, type species to Argeiinae. Mitochondrial phylogenomics also suggested that B. hippolytes was close to Argeiinae. We also found a novel gene order in B. hippolytes compared to other isopods. Conclusions: Bopyroides hippolytes should be excluded from the Bopyrinae and has a close affinity with Argeia pugettensis based on molecular and morphological data. The conserved syntenic blocks of mitochondrial gene order have distinctive characteristics at a subordinal level and may be helpful for understanding the higher taxonomic level relationships of Isopoda. [ABSTRACT FROM AUTHOR]

Freshwater mussels provide important functions and services for aquatic ecosystems, but populations of many species have been extirpated. Information on biodiversity plays an important role in the conservation and management of freshwater mussels. The Xin River Basin is a biodiversity hotspot for freshwater mussels in China, with more than 43 species known, but populations of which are decreasing. Here, we quantify the diversity of freshwater mussels in the middle and lower reaches of the Xin River Basin and study the correlation of habitat characteristics and freshwater mussel diversity. Compared to the historical period, the number of species, density, and biomass of freshwater mussels decreased 33%, 83%, and 82% in the current period, respectively. Fifty two percent of recorded species were empty shells, and 14 native freshwater mussels were not found in the study area. Four species are currently listed as vulnerable species using IUCN criteria and their global status. The assemblage structure of freshwater mussels exhibits significant spatial differences, and there was a correlation with substrate and physicochemical parameters. The main tributary of the Xin River with higher freshwater mussel diversity should be established as one large protected area because the nestedness component was the main pattern of beta diversity. These results indicated freshwater mussel diversity was declining rapidly, which can help focus conservation effort for freshwater mussel biodiversity. [ABSTRACT FROM AUTHOR]

The Yangtze River drainage in China is among the most species rich rivers for freshwater mussels (order Unionida) on Earth with at least 68 species known. The freshwater mussels of the Yangtze River face a variety of threats with indications that species are declining in abundance and area of occupancy. This study represents the first analyses of the genetic structure and diversity for the common and widespread freshwater mussel Nodularia douglasiae based on microsatellite DNA genotypes and mitochondrial DNA sequences. Phylogenetic analysis a fragment of the COI mitochondrial gene indicated that N. douglasiae collected from across the middle and lower Yangtze River drainage are monophyletic with N. douglasiae from Japan, Russia, and South Korea. The results of the analysis of both the mtDNA and microsatellite datasets indicated that the seven collection locations of N. douglasiae in the middle and lower Yangtze River drainage showed high genetic diversity, significant genetic differentiation and genetic structure, and stable population dynamics over time. Moreover, we found that the connections among tributaries rivers and lakes in the Yangtze River drainage were important in maintaining gene flow among locations that N. douglasiae inhabits. An understanding of the genetic structure and diversity of a widespread species like N. douglasiae could be used as a surrogate to better understand the populations of other freshwater mussel species that are more rare in the Yangtze River drainage. At the same time, these results could provide a basis for the protection of genetic diversity and management of unionid mussels diversity and other aquatic organisms in the system. [ABSTRACT FROM AUTHOR]

Biomphalaria straminea is an invasive species in China and is one of the intermediate hosts of Schistosoma mansoni which results in the spread of schistosomiasis. Herein, we firstly report the complete mitochondrial genome of B. straminea. The full length of the mitochondrial genome is 13,652 bp. It consists of 37 typical animal mitochondrial genes, comprising 13 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes. The contents of each base in the complete mitochondrial genome are 33.28% A, 42.01% T, 10.85% C, and 13.87% G, with a high A + T content of 75.29%. Phylogenetic analysis showed that the relationship of B. straminea and Biomphalaria tenagophila was more closed. [ABSTRACT FROM AUTHOR]